I think the key here is twofold. First “the cloud” as commonly understood isn’t what anyone here is talking about. The subject is commercial inference providers.

The “cloud”, or Commercial offerings in storage, VMs, etc are reasonably “secure” in a very general context these days, that is generally true.

OTOH “cloud” AI (commercial inference) is going to use your data for training, incorporating your business processes and domain specific competencies into its innate capabilities, which could eventually impact your value proposition. Empirically, this will happen, eventually, regardless of the user agreement that you signed.

Leakage of proprietary competencies is what is meant by being insecure, in this context.

Second, “cloud isn't secure enough for the enterprise” should be replaced with “enterprise actually cares about security except as a cost/benefit analysis”.

Sending your data to someone else’s data center is a really good way for your data to potentially end up on someone else’s computer. In fact, it’s pretty much the point. If security was the priority, they wouldn’t do that.

Some quant-heads endorsing the latest fad doesn't prove anything. Also they don't care if chinese hackers are vacuuming data cause ballstreet doesn't care about sustainability. But I grant you that secure and trust are just words that don't mean anything anymore anyhow.